The present invention relates to an acoustic lens and an ultrasonic probe using the lens, and in particular relates to an acoustic lens in which the ultrasonic propagation loss is minimized.
An ultrasonic probe is used as an ultrasonic echo sounder transducer, for example in medical ultrasonic diagnostic equipment. As one such ultrasonic probe, there is one where piezoelectric elements are arranged in the widthwise direction of the ultrasonic probe and electronic scanned, and further an acoustic lens having curvature in the lengthwise direction is adhered thereto so as to improve the resolution.
FIG. 4 is a transverse cross-sectional view of a conventional example of an ultrasonic probe described below, while FIG. 5 is a longitudinal cross-sectional view thereof.
As shown in FIG. 4 and FIG. 5, the conventional ultrasonic probe comprises; a piezoelectric element group 10, a backing material 20, an acoustic matching layer 30, and an acoustic lens 40. The piezoelectric element group 10 comprises a plurality of piezoelectric elements 10a having driving (exciting) electrodes (not shown) on opposite main surfaces, and arranged in the widthwise direction on the backing material 20. The backing material 20 has a damping function, for example, prevents the tailing (ringing) of the occurring ultrasonic vibration.
The acoustic matching layer 30 is provided on the upper surface of the piezoelectric elements 10a, and acoustically matches with a specimen (living body). However, the acoustic matching layer 30 becomes unnecessary if the acoustic impedance with the specimen (ore body) is similar.
The acoustic lens 40 is made for example, from silicone rubber in which the acoustic propagation velocity is slower than for the specimen, and comprises, as shown in FIG. 5, a lens portion 40a, and leg portions 40b. The lens portion 40a as shown in FIG. 5, has curvature in the lengthwise direction. The leg portions 40b are planar in shape and are formed with the opposite end sides in a bent L-shape. The lens portion 40a and the leg portions 40b are integrally formed by injecting a silicone rubber into a mold or the like.
The acoustic lens 40 converges the ultrasonic waves radiated from the lengthwise direction of the piezoelectric elements 10a, into a beam, so as to improve the resolution in the lengthwise direction. Reference symbol 50 in FIG. 5 denotes synthetic resin filled between the opposite end faces of the piezoelectric element group 10, and the inside of the leg portions 40b of the acoustic lens 40 (refer to Japanese Unexamined Patent Publication (TOKKYO KOKAI (Japanese Laid-Open Patent Publication) No. Hei9-191497).
However, such a conventional ultrasonic probe has a problem of desensitization caused by the acoustic lens 40. That is, as shown in FIG. 5, the acoustic lens 40 comprises the lens portion 40a having curvature. and the planar leg portions 40b. These leg portions 40b prevent liquids such as chemicals or the like from entering the acoustic matching layer 30, or the piezoelectric elements 10a, from the outside, or facilitate the positioning of other members with respect to the piezoelectric element 10a. 
Accordingly, the height (thickness) of the acoustic lens 40 is increased due to the thickness of the planar portion of the leg portions 40b. On the other hand, the silicone rubber used for the acoustic lens 40 has a large ultrasonic propagation loss. Therefore, due to such a structure, there is a problem of desensitization of the ultrasonic probe as a whole, by increasing the ultrasonic propagation loss due to the acoustic lens 40 over and above what is necessary.
The present invention has an object of providing an acoustic lens with little ultrasonic propagation loss, and an ultrasonic probe using the lens, for which excellent sensitivity is maintained.